1. Technical Field
The present disclosure relates to flow control, and in particular, to devices that operate very rapidly in high pressure environments. One example is a valve for controlling flow of a high-energy pressurant during impulse thrust of rocket or jet engines such as those used in high-speed air and space flight vehicles.
2. Discussion of the Art
Fast acting flow control valves are required for a variety of applications, including applications critical to the control of rocket or jet powered vehicles, missiles or other craft. Commonly, thrusters are used to control propulsion and attitude (e.g., pitch, yaw and roll) of such craft. The thrusters can also be used to reverse thrust to slow or aid in landing the craft. Typically, the thrusters receive high pressure gas from a solid or liquid propellant source. Depending on the specific application, the thrusters can operate for longer sustained durations or in very short bursts, or impulses, of a few seconds or less. Impulse thrusters, as they are called, are required to operate and shut-off nearly immediately upon demand, for example, so that precise flight control can be achieved or to provide instantaneous back-up thrust in the event of main thruster failure.
U.S. Patent Application Publication 2010/0038565 discloses a propellant gas control valve that couples to a thrust nozzle. This valve includes a pilot stage with a pilot flapper valve and actuator and a main stage with a main piston valve and actuator. The pilot and main stages interact via a control pressure port such that below a threshold pressure, associated with short duration flow commands, only the pilot valve is activated and above the threshold pressure, associated with long duration flow commands, both the pilot and main stage valves are activated. A small passage leads from the pilot stage to the outlet to provide low flow propellant pulses when the main stage is de-activated. However, when the main stage is activated, high-rate propellant can flow from the valve. The valve thus works in two modes to supply propellant for low to high thrust values, for example 2-20 lbf, with relatively fine impulse resolution (low minimum impulse bit) during low flow operation.
U.S. Pat. No. 4,826,104 discloses a thruster control valve having an electromagnetically controlled piston valve as the primary flow control valve. The valve can be mounted either at or remote from the combustion chamber of the rocket, and the actuator can be located at or remote from a valve controlling flow to the piston chamber. In the latter case, the disclosed valve has a poppet attached to an elongated plunger that is driven by a solenoid. The poppet has two seats that work to alternately close off supply or exhaust ports leading to/from the piston chamber. The normally de-energized solenoid positions the poppet to engage the exhaust seat so that supply pressure can seat the piston to close off the thrust nozzle. Energizing the solenoid moves the poppet into engagement with the supply seat, which first allows the piston chamber to vent and then allows the piston to unseat from the thrust nozzle so that pressure flow from the combustion chamber can pass through the thrust nozzle.
Still there remains a need for a control valve that provides better response to activation and deactivation command signals. The published application mentioned above is concerned with bi-modal operation to achieve a wide range of thrust values with fine resolution during low flow operation. However, this technique adversely affects the responsiveness of the valve because of the delays associated with the initial low flow stage. The '104 patent, on the other hand, discusses achieving faster operation times by mounting the valve in the combustion chamber, however acknowledges inherent electrical, mechanical and pneumatic delays in the remote actuator construction described above arising from pressurization and depressurization of the piston chamber and the “dead volume” of the actuator arrangement.